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Bedding strength is one of the key factors affecting the propagation of hydraulic fractures through beddings, which is mainly determined by cohesion, internal friction angle and tensile strength. However, there are few researches on this. Therefore, in order to further study the influence mechanism of bedding strength on the propagation of hydraulic fractures through beddings. Based on the three-dimensional block discrete element method, this paper simulated the propagation morphology of hydraulic fractures under different cohesion, tensile strength and internal friction angle. The simulation results show that bedding cohesion has a significant influence on the propagation of hydraulic fractures through beddings. Under low cohesion, hydraulic fractures mainly shows transverse propagation, accompanied by a larger degree of bedding activation, however, at high bonding strength, the permeability of hydraulic fractures is strong, and the propagation is nearly circular. The tensile strength of bedding has no obvious effect on the propagation capacity of hydraulic fracture and can be ignored in practical engineering. The penetration of hydraulic fractures increases with the increase of internal friction angle, and the hydraulic fractures are easy to diffuse along bedding at low internal friction angle.

China possesses abundant coal resources and has extensive potential for exploitation. Nevertheless, the coal rock exhibits low strength, and the coal seam fractures due to mining activities, leading to an increased rate of gas emission from the coal seam. This poses significant obstacles to the exploration and development of the coal seam. This paper focuses on studying the failure mechanism of fractured coal rock by conducting uniaxial and triaxial compression experiments on the coal rock found at the Wangpo coal mine site. Simultaneously, in conjunction with the findings from the field experiment, a gas migration model of the mining fracture field is constructed to elucidate the pattern of coal seam gas distribution during mining-induced disturbances. The study structure reveals that coal rock exhibits three distinct failure modes: tensile failure, shear failure, and tension-shear failure. The intricate fissure in the rock layer will intensify the unpredictability of rock collapse patterns. The compressive strength of coal rock diminishes as the confining pressure drops. The coal rock in the working face area will collapse as a result of the lack of confining pressure. In the rock strata above the mining fracture zone, the gas pressure is first higher and then significantly falls with time. After 100 days of ventilation, the low gas pressure area changes little, so to ensure the safety of the project, the ventilation time of the fully mechanized mining surface is at least 100 days. The research results will help to establish the core technology system of coal seam development and improve the competitiveness of coal seam resources in China. [ABSTRACT FROM AUTHOR]

It is crucial for the successful development of fractured reservoirs to understand the interaction behavior between hydraulic fractures and natural fractures. This work employed a true-triaxial fracturing experiment using prefabricated samples with natural fractures, along with a three-dimensional (3 D) numerical model, to investigate the interaction mechanisms between hydraulic fractures and preexisting natural fractures. Various influencing factors, including the horizontal stress difference, injection rate, fluid viscosity, and approach angle, are considered. The results reveal three distinct modes of interaction between hydraulic fractures and natural fractures: crossing, deflection, and arrest. As the horizontal stress difference, injection rate, and viscosity increase, the interaction between hydraulic and natural fractures undergoes a gradual shift, evolving from arrest to deflection and ultimately crossing. A smaller approach angle enhances the likelihood of hydraulic fractures being captured by natural fractures. Furthermore, the evaluation criterion of propagating ability is proposed based on the dimensionless value to facilitate the evaluation of the interplay between hydraulic and natural fractures. The interaction behavior diagrams between hydraulic fracture and natural fracture in different regimes is established. It shows that the fracture penetration capacity gradually increases from toughness-dominated regime to viscous-dominated regime, as evidenced by the phased arrangement of arrest, deflection, and crossing in their interaction with natural fractures. When the tensile strength and cohesion of natural fractures is high, hydraulic fractures tend to pass through directly, while conversely, they are easily arrested by natural fractures. The research findings can offer valuable insights for optimizing the fracturing in unconventional reservoirs with developed natural fractures. [ABSTRACT FROM AUTHOR]